1. Field
The disclosed embodiments relate to resonant gate drive circuits. More specifically, the disclosed embodiments relate to resonant-recovery power reduction techniques for pulse generation.
2. Related Art
When a voltage source V is used to charge a capacitive load to a charge Q, it supplies energy U=QV, some part of which is stored in the capacitive load while the rest is dissipated. For the case of complete charging and a linear capacitance C, Q=CV, and the energy supplied is U=CV2, while the energy stored is only Ucap=½CV2. The stored energy is dissipated when the capacitance is switched to ground, so the switching loss per cycle is all of the supplied energy, giving an average power loss for switching frequency f of:Ploss=fQV  (1)Complete charging of a linear capacitance obtains the usual result:Ploss=fCV2  (2)
As a prime example of where such losses come into play, the energy consumed switching the capacitive load presented by the gate of a power metal-oxide-semiconductor field-effect transistor (MOSFET) can limit the efficiency of switch-mode DC-DC converters. Not only does the gate drive contribute to the losses, but since it and other switching losses also grow with frequency, the losses associated with inductive or capacitive energy-storing components in a converter are constrained to be greater than they otherwise could be. For example, for a simple boost converter the losses associated with its inductor are reduced as the frequency is increased, since the ripple current decreases (provided that the switching frequency is not increased to the point that a permeable core used in the inductor exhibits a substantial phase lag in its response). Higher frequency operation also allows for further optimization of the inductor within a fixed volume constraint to trade off ohmic resistive loss and any core losses.
Although there are other switching losses in these converters that need attention, the gate drive loss is often a substantial part of the switching loss. What is needed is a method that can switch the gates without losing all the energy supplied to them.